A backlight device used in a so-called liquid crystal TV (television) is known to have a configuration including a blue LED chip which emits blue light as primary light, a red phosphor which is excited by the blue light to emit red light as secondary light, and a green phosphor which is excited by the blue light to emit green light, and also known to have a configuration including a blue LED chip, a green LED chip which emits green light, and a red LED chip which emits red light. Such backlight device emits white light by mixing colors of blue light, green light, and red light. In recent years, there has been a tendency to extend the color reproduction range that is able to be displayed by a liquid crystal TV, and it has been considered that the latter configuration including the blue LED chip, the green LED chip, and the red LED chip is more desirable in order to realize a high color reproduction range.
However, the latter configuration has a problem that since the blue LED chip, the green LED chip, and the red LED chip have characteristics different from each other, a color shift occurs and it is difficult to maintain white balance.
PTL 1 discloses a configuration in which light quantities of three (red, green, and blue) backlights are measured by three optical sensors and the measured values are compared with set values and subjected to operations so that white balance is maintained at all times regardless of a temperature change or a change over time.
PTL 2 discloses a configuration including light emitting diodes of three colors of red, green, and blue, color sensors corresponding to the respective light emitting diodes, a temperature sensor for measuring temperatures of the light emitting diodes, a control operation unit which corrects a chromaticity change caused by the temperatures of the light emitting diodes and a chromaticity change caused when controlling the brightness of red, green, and blue of the light emitting diodes, and maintaining luminance and chromaticity desirably.
PTL 3 discloses a light emitting element which exhibits white light by exciting a divalent Eu-activated CaAlSiN3 (hereinafter, referred to as a “CASN phosphor”) which is a nitride phosphor exhibiting red light emission and a green phosphor exhibiting green light emission with a blue LED emitting blue light.
As a phosphor exhibiting green light emission, for example, a Eu-activated β-SiAlON phosphor indicated in PTL 4 has been conventionally used preferably.
In a case where an illumination device which emits white light by combining a blue LED, a red phosphor, and a green phosphor is used as a backlight light source of a liquid crystal TV, color reproducibility of the liquid crystal TV is likely to be improved by using a phosphor having a narrower peak wavelength of a light emission spectrum.
Thus, in order to realize a display device, such as a liquid crystal TV, capable of displaying deep red, a backlight device indicated in PTL 5 using a Mn4+-activated K2SiF6 phosphor (hereinafter, referred to as a “KSF phosphor”), a green phosphor, and a blue LED chip has been developed. The KSF phosphor has a spectrum of peak wavelength narrower than that of the CASN phosphor and is able to improve color reproducibility more than before.